Long-term Dynamical Evolution of Pallene (Saturn XXXIII) and its Diffuse, Dusty Ring

TL;DR

This study investigates the long-term dynamical evolution of Pallene and its dusty ring around Saturn, revealing that Pallene is not currently in resonance with major moons and that non-gravitational forces significantly influence ring particle behavior.

Contribution

The paper provides a comprehensive numerical analysis of Pallene's orbital evolution, resonance status, and the dynamics of its ring particles, incorporating gravitational and non-gravitational forces for the first time.

Findings

Pallene is not in mean motion resonance with major moons for up to 5 Myr.

Non-gravitational forces cause vertical excursions and outward migration of ring particles.

The ring's steady state depends on the size distribution of particles and Pallene's mass production rate.

Abstract

The distinctive set of Saturnian small satellites, Aegaeon, Methone, Anthe, and Pallene, constitutes an excellent laboratory to understand the evolution of systems immersed in co-orbital dusty rings/arcs, subjected to perturbations from larger satellites and non-gravitational forces. In this work, we carried out a comprehensive numerical exploration of the long-term evolution of Pallene and its ring. Through frequency map analysis, we characterised the current dynamical state around Pallene. A simple tidal evolution model serves to set a time frame for the current orbital configuration of the system. With detailed short and long-term N-body simulations we determine whether Pallene is currently in resonance with one or more of six of Saturn's major moons. We analysed a myriad of resonant arguments extracted from the direct and indirect parts of the disturbing function, finding that Pallene is not in mean motion resonance from the present up to 5~Myr into the future; nonetheless, some resonant arguments exhibit intervals of libration and circulation at different timescales and moon pairings. We studied the dynamical evolution of micrometric particles forming the ring, considering gravitational and non-gravitational forces. Non-gravitational forces are responsible for particles vertical excursions and outward migration. By estimating the satellite's mass production rate, we find that Pallene could be responsible for keeping its ring in steady-state only if it is mainly composed of large micrometre-sized particles. If mainly composed of particles with a few micrometres for which Pallene is the only source, the ring will spread out, both radially and vertically, until it finally disappears.